I did a world update which included a zfs upgrade, after the reboot no zpool was available anymore. So I've tried to recompile the kernel, which failed. Then I decided to upgrade the kernel, from 3.10.17 to 3.14.14, still no luck.

Late to the party... But I do find when I do ZFS upgrades on NFS box (running Arch) I sometimes need to re-import the ZFS pool with the -force flag as ZFS complains the Hostid has changed and won't load the pool. You will see an error message like that in the boot logs.